Sleep and Clock Phenotypes in Worldwide Population Genetics Studies

*Corresponding author e-mail: karla.allebrandt@med.uni-muenchen.de Despite of its complexity, sleep has two straightforward properties — timing and duration, which are influenced by a homeostatic process (how long have we been awake) and a circadian process. Individual circadian clocks entrain differently to environmental cycles ( zeitgebers , e.g., light and darkness), earlier or later within the day, leading to different chronotypes. To assess chronotype and sleep duration in humans, we ask timing of sleep (independently for the workweek and weekends) using the Munich Chronotype Questionnaire (MCTQ). In the 12 populations we have assessed so far, the distribution of chronotypes and sleep duration form population-specific bell-shaped curves ranging from extreme early to extreme late types (Gaussian distributions are characteristic for multi-factorial traits). Although the genetics of sleep has been addressed in humans, associations between clock genes and sleep duration or timing have never been investigated systematically. To further understand this genetic influence in humans, we are using advanced methods of genomics in association studies with chronotype or sleep duration as phenotypes. Our first results indicate that the investigated traits have a genetic component, and that genes (beyond the known clock and sleep candidate genes) play a role in the molecular mechanisms modulating sleep timing and duration. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil